California is about to dramatically increase the amount of information it makes public about the state's groundwater.

Under new legislation signed by Gov. Jerry Brown last week, the state will begin making available well drilling reports that have been kept confidential for decades. That will open up a trove of information about the construction of approximately 800,000 wells for scientists and others who are seeking detailed data to better analyze California's drought-stressed water supplies.

"Now that we have this data and these tools, we can finally start managing our groundwater resources properly, and that's huge," said Deborah Ores, an attorney and legislative advocate in Sacramento for the Community Water Center, which focuses on areas of the Central Valley where wells have been going dry and people have been struggling for years with contaminated water supplies.

Until now, California had been the only western state that prohibited the release of reports submitted by well drillers. In other states, those well drilling logs have long been publicly available.

The secrecy began in California in 1951, just two years after the Legislature first required well drillers to start filing the reports. That change was adopted at least in part because some drillers at the time wanted the information not to be divulged, apparently because they didn't want competitors to have details about their operations.

The new measure requires that the records be made available to the public upon request. It was passed as part of Senate Bill 83, a trailer bill that Brown signed together with the state budget.

Since 2011, Sen. Fran Pavley (D-Agoura Hills) had repeatedly proposed bills aimed at opening up the well reports to the public.

Water scientists supported the change, saying that having more information about wells will help in efforts to manage California's groundwater.

"This is going to be an important step forward and a very essential data piece to help us manage the resource, both from a water quality and from a water quantity perspective," said Thomas Harter, a groundwater hydrologist at the University of California, Davis. "It'll be important for us to better understand the architecture of our aquifers."

California already makes public its data on groundwater levels measured in certain wells across the state. The well logs, which are kept by the state Department of Water Resources, provide other sorts of information that drillers must submit to the state each time they construct a well.

Each report includes information such the geological layers found during drilling, the depth of the well, the water level at the time and the depth of the well screen – the filtering device where water is drawn out.

"It'll be much easier in the future to link water quality data to the actual depth from which water samples were collected," Harter said. "So we can actually map water quality in three dimensions rather than just in two dimensions."

He said having the additional data will also be useful as agencies develop long-term plans to manage aquifers under California's new Groundwater Sustainability Management Act, which Brown signed into law last year. That legislation lays out a statewide strategy for protecting groundwater, putting local agencies in charge while also giving the state new authority to step in when necessary to stabilize declining aquifers.

Ores said the information in the well logs will also be helpful in areas where communities are looking for new water sources and where portions of the groundwater are tainted with hazardous contaminants such as nitrates or arsenic.

"We can look at these well logs and look at where are there areas that are pumping safe water," Ores said. "And you can use that information to figure out where a new well can be drilled so a community can get that safe water."

Some farming groups and agricultural water districts in the Central Valley opposed opening up the well logs. They argued the change would infringe on private property rights, would lead to lawsuits and could give away the locations of well sites to metal thieves looking to steal pieces of water infrastructure. Harter said he thinks those fears are unjustified.

The state Department of Water Resources has said it plans to make public the locations of wells while redacting the names and personal addresses of well owners.

"The issue that will arise is when the well location and the owner's address are the same," Ores said. "But even if we could get approximate locations of where wells are, it is still extremely beneficial to understanding groundwater basins. Because if it's within a quarter mile or so, you're still going to understand what the basin looks like."

But something else is: a vast repository of state records that scientists and water policy specialists say could dramatically improve our understanding of California’s groundwater resources if they were made public.

The records are called well completion reports, or well logs for short. For decades, the California Department of Water Resources has gathered the documents from well drillers and archived them in cardboard boxes in West Sacramento and other locations around the state.

In all other western states, such reports are public and often searchable online. But in California, they are considered confidential under a 64-year-old state law. Many think that should change.

Access to logs could help improve water quality and reveal which parts of California are being pumped the most, experts believe. Laurel Firestone, co-executive director of the Community Water Center, a Visalia-based nonprofit, called the secrecy a huge impediment to understanding the state’s groundwater system.

“It’s almost like when they black out classified information,” Firestone said. “We have no maps of where people are using water, and what people are using water for. It’s hugely important. We work with families that have lost their entire water supply, whose wells are going dry.”

Opening the state’s well log vault is under consideration this spring at the state Capitol, where lawmakers, the governor and state officials are scrambling to find ways to help California cope with a four-year drought that is straining surface and groundwater supplies. Earlier this month, NASA senior water scientist Jay Famiglietti warned that “the state has only about one year of water supply left in its reservoirs, and our strategic backup supply, groundwater, is rapidly disappearing.”

State Sen. Fran Pavley, D-Calabasas – author of two of three historic groundwater laws passed by the Legislature last year – has introduced a new bill to make well logs public. A hearing is scheduled for today.

“After four years of a continuous drought, it is about time we get this information … to better protect California’s precious groundwater,” said Pavley in a statement.

To a nonspecialist, well logs can appear as dry as the drought-parched California earth. To groundwater scientists, they are a treasure trove of information that can help chart the size, shape and thickness of aquifers and determine how water cycles through and between them. That, in turn, can help predict how much pumping aquifers can withstand without being depleted.

The state’s stockpile of well logs has grown to about 800,000 documents over the past six decades. Laid end to end, that is enough paper to circle Lake Tahoe twice.

While the public can’t view those records, the Legislature did create a loophole in 1951 allowing access “to government agencies for use in making studies,” making them accessible to some professionals but not others. The passage has been so narrowly interpreted by the Department of Water Resources that even scientists who work for public universities sometimes can’t gain access.

This is the third time since 2011 that Pavley – chair of the Senate Natural Resources and Water Committee – has sought to make well logs open to the public. Whether she will succeed this year is anyone’s guess. But it is certain the debate will be lively.

A glimpse of the coming drama can be gleaned from letters that have arrived in her office in recent weeks.

East Bay Municipal Utility District, which provides water to more than a million people, wrote to support the bill, saying data in well logs “is central to developing and implementing groundwater management plans.”

But in a state where groundwater is tied to private property rights and farmers pump with no restrictions, opposition remains strong in the agricultural community.

“We believe the well log data is available to those entities that have a genuine need to evaluate and utilize it,” wrote representatives of three agricultural organizations and the California Chamber of Commerce, in a letter opposing the Pavley bill.

“No beneficial purpose could be gained by making this confidential data available to the public,” they added. “We believe this measure will only assist those trolling for lawsuits.”

Several environmental and community action groups wrote in support. “As the physical effects of the drought worsen, from loss of water supplies to increased concentrations of groundwater contaminants, the need for reliable and transparent data … grows,” they said. “The information contained within well completion reports would allow communities to identify new well locations that might yield safe drinking water, a concern affecting thousands across the state.”

The governor’s view is already well known. “California is the only western state that does not provide ready access to well reports,” he wrote in a statement vetoing a 2011 well log access bill he felt was too restrictive. “That should be changed.”